Fifty million Americans have hypertension or are taking antihypertensive medications. Both mortality and morbidity from cardiovascular diseases show a positive association with the level of arterial pressure. In fact, the rate of death from all causes increases proportionally to an increase in the level of arterial pressure. Therefore, interventions which lower arterial pressure are being vigorously investigated. Recently it has been shown that a single bout of dynamic exercise reduces arterial pressure for several hours in individuals with hypertension. The reduction in arterial pressure following exercise is most often associated with no change or a reduction in heart rate and muscle sympathetic nerve activity. These results suggest an exercise induced alteration in baroreflex function. Therefore, this proposal is designed to examine the effects of a single bout of dynamic exercise on the arterial and cardiopulmonary baroreflex regulation of the cardiovascular system. Specifically, this proposal is designed to test the hypothesis that a single bout of dynamic exercise attenuates the arterial baroreflex regulation of directly measured sympathetic nerve activity. In addition, a single bout of dynamic exercise may enhance the direct inhibitory influence of the cardiopulmonary baroreflex and the interaction of the cardiopulmonary and arterial baroreflex on the regulation of sympathetic nerve activity. The underlying hypothesis is that the tonic inhibitory influence of the cardiopulmonary baroreflex on the sympathetic nervous system, arterial baroreflex and hormonal regulation is enhanced as a result of a single bout of dynamic exercise. These studies will provide a better understanding of the regulation of the neurohumoral drive to the circulation and the effect of a single bout of dynamic exercise on this regulation. Because it has previously been reported that gender influences the autonomic responses associated with a single bout of dynamic exercise, comparisons will be made between male and female spontaneously hypertensive rats.